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1、DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General
2、Chemistry for Engineering Undergraduates第四章第四章 溶液中的离子平衡溶液中的离子平衡 Equilibrium in SolutionDR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中
3、的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates弱酸和弱碱的解离平衡弱酸和弱碱的解离平衡一元弱酸、弱碱的解离平衡多元弱酸、弱碱的解离平衡DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUH
4、AN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates一元弱酸、弱碱的解离平衡一元弱酸、弱碱的解离平衡设一元弱酸初始浓度为c，在水中电离度为a： c(1-a)cacaHXH+ + X-若于是稀释定律：溶液被稀释时，电离度a 增大。H
5、+浓度简化计算公式DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates
6、 General Chemistry for Engineering Undergraduates计算实例计算实例【解】【例】计算298K时，0.100moldm-3 HAc溶液的解离度a和氢离子浓度。已知 。c(1-a)cacaHAcH+ + Ac-由于近似计算精确计算结果1.314%H+浓度 c(H+) = ca a = 1.323 x 10-3 moldm-3DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GE
7、OSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates多元弱酸、弱碱的解离平衡多元弱酸、弱碱的解离平衡多元弱酸弱碱分步解离，每一步都有相应的解离平衡。例如： 1. H2S + H2OH3O+ + HS-2.
8、 HS- + H2OH3O+ + S2-由于在H2S水溶液中，H3O+离子主要来源于第一步解离，第二步解离出来的少量H3O+可以忽略不计。可以按一元弱酸处理可求出H3O+离子浓度。DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C
9、溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates于是在H2S水溶液中，c(S2-)约等于H2S的第二步解离常数。将H2S的二个解离反应相加，得H2S + 2H2O2H3O+ + S2-H2S浓度一定时，调节溶液酸度，可以控制S2-的浓度。利用硫化物沉淀分离金属离子时常用到这一规律。DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND
10、 CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates计算实例计算实例I 见教材
11、见教材P98 例例4-2本节主要结论多元弱酸的解离是分步进行的，一般 。溶液中的 H+主要来自于弱酸的第一步解离，计算 c(H+)或 pH 时可只考虑第一步解离。对于二元弱酸 ，当 时，c(酸根离子) ，而与弱酸的初始浓度无关。对于二元弱酸 ，当c(弱酸)一定时，c(酸根离子)与 成反比。DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 43
12、0074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates计算实例计算实例II【例】计算0.01 moldm-3 H2CO3溶液中的H3O+、H2CO3、HCO3-、CO32-和OH-的浓度及溶液的pH值。已知 【解】首先考虑第一步解离。设HCO3-的浓度为x moldm-3H2CO3
13、+ H2OH3O+ + HCO3- 10.010-xxx则求得DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engi
14、neering Undergraduates General Chemistry for Engineering Undergraduates考虑第二步解离，设CO32-的浓度为y moldm-3HCO3- + H2OH3O+ + CO32- 26.5x10-5+yy6.5x10-5-y近似求得 ，OH-来自于H2O的解离平衡，设其浓度为z moldm-3 H2O + H2OH3O+ + OH-6.5x10-5+y+zz近似求得DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY L
15、ABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates缓冲溶液缓冲溶液 Buffer Solution同离子效应缓冲溶液缓冲溶液的pH值计算缓
16、冲溶液的配制DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates Ge
17、neral Chemistry for Engineering Undergraduates计算实例计算实例【例】298K时，0.1 dm3 的0.01 mol dm-3 HAc溶液中，加入0.020 mol NaAc固体，求此溶液HAc的解离度a。 【解】c(HAc)=0.10 moldm-3 c(NaAc)=0.20 moldm-3NaAc是强电解质，在溶液中全部解离成Na+离子与Ac-，设平衡时H+浓度为x，则各组分物质的浓度为：0.1-xx0.2+xHAcH+ + Ac-比较：0.1 moldm-3 HAc的解离度a =1.314在弱电解质溶液中，加入具有相同离子的强电解质，使得弱电解
18、质解离度降低的现象，叫同离子效应。DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Underg
19、raduates General Chemistry for Engineering Undergraduates缓冲溶液缓冲溶液当加入少量强酸，强碱或稀释时，保持pH值基本不变的溶液称为缓冲溶液，一般由弱酸与其共轭碱(如HAcNaAc)、或弱碱与其共轭酸(如NH3H2ONH4Cl) 组成。缓冲溶液与非缓冲溶液的比较缓冲溶液与非缓冲溶液的比较缓冲溶液的作用是使溶液的pH值保持恒定，对生命的产生与进化具有重要意义，因为多数生物都只能在一定pH范围内生长，例如血液pH=7.357.45，H2PO4-HPO42-, H2CO3NaHCO3。DR. ZHOU CHENGGANG : FACULTY O
20、F MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Unde
21、rgraduates缓冲作用原理缓冲作用原理HAcH+ + Ac-以HAc- NaAc为例： 加入少量酸，大量的Ac与外加的H+结合成HAc，平衡左移。而 HAc解离度很小，所以c(H+) 基本不变， Ac-起抗酸作用。加入少量碱， H+与外加的OH-结合成H2O，平衡右移， HAc进一步解离，所以c(H+) 基本不变， HAc起抗碱作用。+ OH- H2ODR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCI
22、ENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates缓冲溶液的缓冲溶液的pH值计算值计算弱酸与其共轭碱形成的缓冲溶液：HXH+ + X-两边取负对数得于是DR. ZHOU CHENGGANG : FACULTY
23、OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Und
24、ergraduates弱碱与其共轭酸形成的缓冲溶液(NH3H2ONH4Cl)：NH3 + H2ONH4+ + OH-两边取负对数得于是DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in
25、 Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates计算实例计算实例 I【例】计算0.1 moldm-3 HAc和0.1 moldm-3 NaAc的混合溶液的pH值。将该溶液适当稀释或浓缩，pH值如何变化？ 【解】稀释或浓缩时 按比例同时降低或升高，因此溶液的pH值保持不变。 DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENER
26、GY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates计算实例计算实例 II【例】在0.1 moldm-3 HAc和0.1 moldm
27、-3 NaAc的混合溶液中，加入0.001 dm3的1.0 moldm-3 NaOH溶液，计算此时溶液的pH值。【解】HAc + NaOHNa+ + Ac- + H2ODR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子
28、平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates计算实例计算实例 III【例】在0.1 moldm-3 HAc和0.1 moldm-3 NaAc的混合溶液中，加入0.001 dm3的1.0 moldm-3 HCl溶液，计算此时溶液的pH值。【解】HAcH+ + Ac-DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SU
29、STAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates缓冲溶液的配制缓冲溶液的配制缓冲溶液中加入少量强酸、
30、强碱时，pH值可维持不变，但如加入过多的酸或碱时，缓冲溶液将失效，衡量其缓冲能力大小的尺度称之为缓冲容量。配制一定pH值的缓冲溶液，可选用 与pH相近的酸及其共轭碱或 与pOH相近的碱及其共轭酸，并且共轭酸碱对浓度比应接近1，共轭酸碱对的浓度大一些。 例如：需pH=46的缓冲溶液，应选用 =46的弱酸及其共轭碱，可选用HAcNaAc。例如：需pH=910 的缓冲溶液，应选用 =54的弱碱及其共轭酸，可选用NH3H2ONH4Cl。(pOH=54)DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE
31、ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates共轭酸碱对浓度越大，缓冲容量越大。例如，弱酸和其共轭碱浓度各为1 mol
32、dm-3，增加0.01 mol H+时，例如，弱酸和其共轭碱浓度各为0.1 moldm-3，增加0.01 mol H+时，当酸与碱比值在1/1010/1之间，相应的pH及pOH变化范围：DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化
33、学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates共轭酸碱对浓度比为1时，缓冲容量最大。例如，弱酸和其共轭碱浓度共为1 moldm-3，当二者比值为1:1，溶液中增加0.01 mol H+时，例如，弱酸和其共轭碱浓度共为1 moldm-3，当二者比值为1:99，溶液的pH值为：溶液中增加0.01 mol H+时，DR. ZHOU CHENGGANG : FACULTY OF MAT
34、ERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergrad
35、uates计算实例计算实例【例】用HAcNaAc配制pH4.00的缓冲溶液，求c(HAc)与c(NaAc)的比值。【解】DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-27-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Soluti
36、on General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates常用标准缓冲溶液常用标准缓冲溶液DR. ZHOU CHENGGANG : FACULTY OF MATERIALS SCIENCE AND CHEMISTRY:SUSTAINABLE ENERGY LABORATORY:CHINA UNIVERSITY OF GEOSCIENCES WUHAN:388 LUMO ROAD, WUHAN 430074, HUBEI, CHINA P.R.:+86-2
37、7-6788-3431(OFFICE) 大学化学C 溶液中的离子平衡 Equilibrium in Solution General Chemistry for Engineering Undergraduates General Chemistry for Engineering Undergraduates缓冲溶液缓冲溶液pKa缓冲范围缓冲范围氨基乙酸+HCl2.351.53.0氯乙酸+NaOH2.8623.5甲酸+NaOH3.7734.5HAc+NaAc4.7645.5六次甲基四胺+HCl5.134.56.07.216.58三羟甲基甲胺+HCl8.217.59硼砂9.248.510NH4+NH39.258.510
